1. Field of the Invention
The present invention relates to a radio-frequency (RF) receiver, and more particularly, to a RF receiver and a method of improving sensitivity of a RF receiver by reducing the interference of digital noises.
2. Description of the Related Art
With the advancement of integrated circuits in the telecommunication industry, various electronic devices have been developed. These electronic devices comprise high-power communication devices such as cellular phones, wireless communication devices, or low-power communication devices such as remote-controlled toys.
The 1-GHz low-power CMOS super-regenerative receiver is disclosed in p.440, vol. 36, JSSC, from the Institute of Electrical and Electronic Engineers (IEEE). Wherein, the super-regenerative receiver is fabricated using the complementary metal-oxide-semiconductor (CMOS) technology. The linear mode further offers better selectivity of the receiver. The super-regenerative receiver, however, cannot screen the coupling noise generated from other circuits in the receiver. As the integrated circuit technology is highly developing, if more circuits are integrated in a single chip, the base noise will substantially limit the efficiency of the receiver.
FIG. 7 is a schematic circuit block diagram showing a conventional RF receiver. The RF receiver 70, i.e. the super-regenerative receiver, comprises a RF receiving terminal 702, an oscillating circuit 704, a filter rectifying circuit 706, a slicer circuit 708, a decoding circuit 712, a constant current control circuit 718, an input/output circuit 720, a ring oscillating circuit 716 and a constant current source 714. Wherein, the constant current source 714 is electrically coupled to the voltage source. In the conventional RF receiver 70, the trigger time for the oscillating circuit 704 depends on the intensity of the received signal. Further, the RF receiver 70 converts the inputted RF signal to 1 or 0. After the noise is filtered by the filter rectifying circuit 706, the RF signal is then outputted to the slicer circuit 708. The slicer circuit 708 converts the RF signal from analog into digital data, and outputs the digital data to the decoding circuit 712. Then, the current controller 718 and the input/output circuit 720 output a constant current according to the control signal from the decoding circuit 712 even when different voltages are applied to the integrated circuits. The constant current source 714 provides a constant current to the ring oscillating circuit 716. The ring oscillating circuit 716 provides a sampling frequency to the oscillating circuit 704, the filter rectifying circuit 706, the slicer circuit 708 and the decoding circuit 712.
In the conventional technology, if a noise collides with a received RF signal, and the frequency of two signals are overlapped, the RF receiver 70 cannot identify whether the received signal is 1 or 0. The sensitivity of the RF receiver thus deteriorates. The noise at the RF receiving terminal 702 is a digital harmonic signal. Due to the temperature variations, voltage changes or vibrations, the digital clock may shift, causing the digital harmonic signal to collide with the input signal. As a result, the RF receiver 70 becomes unstable. When the RF receiver 70 in a remote-controlled toy is unstable, the toy cannot be controlled according to the given instructions.